H.323 is a well known standard for multi-media communication. This standard governs communications between terminals and other entities over a packet switched network. A person of ordinary skill in the art and who is familiar with the H.323 standard will understand the elements of establishing third party call control via a Gatekeeper. Briefly, upon powering up, a H.323 endpoint (desktop) implements a discovery process for determining which Gatekeeper to register with. This can be effected in a number of ways, such as by multicasting a message which identifies the endpoint (i.e. the GRQ message) to a predetermined multicast address. The assigned Gatekeeper then responds (i.e. the GCF/GRJ message) with its RAS channel address (i.e. IP address). Before attempting to place a call, the endpoint must register with the Gatekeeper (i.e. the RRQ message) by advising it of its transport address and any aliases (discussed below). Registration is then confirmed by the Gatekeeper (i.e. via the RCF/RRJ message). Actual call signaling takes place over an established channel between two H.323 endpoints using Q.931 messages. For third party (i.e. Gatekeeper) call control, the originating endpoint sends a H.225 Admission Request (ARQ) to the Gatekeeper over the previously established RAS channel. The Gatekeeper responds with an ACF message which specifies the call signaling transport address to use for the call setup. The originating endpoint then transmits a Setup message to the Gatekeeper which, in turn, sends a Setup message to the destination endpoint. The destination endpoint then sends an admission request (ARQ) to the Gatekeeper and receives an acknowledgment (ACF) therefrom. Finally, a Connect message is sent from the destination endpoint to the Gatekeeper which contains the address of the originating endpoint for H.425 control messages to the originating endpoint.
The inventor has recognized the desirability of adapting the H.323 standard to voice communications such as traditionally implemented via a PBX. However, the H.323 umbrella protocol standard only provides a limited set of recommendations in terms of supporting functionally based supplementary services between a Gatekeeper (GK) and an Endpoint (EP), due to the relative newness of the standard. Thus, H.323 suffers from limitations in providing a full range of PBX like functionally based supplementary services. The use of a functionally based supplementary service protocol requires a substantial amount of intelligence and knowledge of state within the Endpoint, which tends to make an Endpoint code heavy.
The H.323 recommendation refers to the H.450 recommendation as the primary method for functionally based supplementary service signaling in the H.323 domain. The H.450 recommendation is new, with support for only eight supplementary services (as of Oct. 99), and expanding at a current rate of only three supplementary services per year. Furthermore, the H.450 protocol is a cumbersome protocol since it is ASN.1 based.
Another available method of supplementary services signaling is through the use of “DTMF signaling”. This is similar to the use of feature access code signaling methods seen in traditional telephony. However, DTMF signaling is also not an ideal method for providing supplementary services since it usually requires a user to remember a complicated set of access codes and is therefore error prone.